Both delta 9-THC and cannabinol (CBD) in high doses significantly increase the turnover rate of GABA in substantia nigra and reduce the turnover rate of acetylcholine in hippocampus and striatum. In hippocampus doses as low as 0.2 mg/kg delta 9-THC but not CBD significantly reduce the turnover rate of acetylcholine. These results suggest that hippocampal cholinergic mechanisms may play a role in the psychotomimetic activity of delta 9-THC.